Lifetime Of LEDs Research Articles

Optimisation of LED luminaires renewal interval based on proposed CLO adjustment method

A considerable part of electrical power is consumed in lighting systems. Electrical power usage and, as a result, generation is proportional to CO2 emissions. CO2 emissions result in climate change. Many countries encouraged people to use modern light sources, including LEDs, to increase the efficiency of lighting systems. An LED, during its long life, is subjected to gradual degradation. Its degradation can be understood from its radiant flux decrement. Some standards, including LM 80-08, addressed this issue. Constant lumen output (CLO) drivers are used to deal with LED degradation issues. There is not much scientific research on the topic of CLO. This paper suggests a scientific approach to finding CLO's exact output voltage as a function of time during the LED lifetime, limiting energy consumption to the required value. Also, a method for finding the best time to replace LED luminaires to minimise the financial burden for the owners has been found. By optimising renewal time for LED luminaires, energy usage (CO2 emission) and end-of-life waste will be managed to the required value. In addition, for use in CLOs, the paper suggests adding more specified data to the LM 80-08 report.

An analytical and machine learning model for SPD estimation and its prediction for lumen and chromaticity shift based LED lifetime performance analysis

The LED lifetime is commonly estimated by manufacturers using an exponential model to evaluate L70 criteria. However, it ignores colour characteristic variation and does not explain the root cause of LED failure. In this paper, a spectral power distribution (SPD) based approach is proposed to estimate lifetime performance of cool white LED considering both colour characteristics and lumen maintenance, as all the lighting performance parameters are extracted from SPD. The exponential model does provide the lifetime using only lumen data and does not explain the colour characteristics. As an alternate to the exponential model, a quadratic polynomial, and machine learning (ML) models with hours and temperature as input factors, is proposed to determine SPD for experimental conditions as well as to predict for other operating conditions. Further, the lifetime performance analysis is performed for reliability assessment conditions through both lumen and colorimetric performances. The outcomes of all the models are analysed and it is found that the results are comparable. As ML models are simpler than analytical models for more than two inputs, further it is used to predict SPD at different temperatures and the LED performance is validated. Further analysis shows that a decrease in blue light is the primary cause of the overall decrease in light output and decrease in yellow emission due to phosphor degradation is the reason for chromaticity shift.

A comprehensive detailed formula for LED degradation and lifetime estimation leading to reduce CO2 emissions

Recently as global warming and (green-house gases) GHG emissions topics have become hot, many countries have pledged for decreasing their carbon footprint in a reasonable time. Since a substantial part of carbon footprint is coupled with electric energy consumption and in turn, a considerable part of consumed electrical energy around the world is related to the lighting, as energy efficient light sources LEDs have attracted notices to themselves. According to long lasting LEDs as semiconductor light sources, they face a great amount of lumen depreciation during their lifetime. Since, besides environmental impact, economic aspects are also of great interest for users, it is important to be able to anticipate the LEDs lifetime as exact as possible. This enables users not only to select the correct LED luminaires by cost-benefit analysis, but also to schedule for renewing them in the right time. As mentioned in former researches LEDs can show better lumen maintenance than what is estimated by prevalent TM 21 standard method. This paper proposes a comprehensive detailed formula for finding LEDs’ more accurate lifetime. The novelty of the research methodology is breaking up the LED to its major parts and by finding each part degradation model and combining them, coming up with the ultimate accurate formula. The proposed formula anticipates longer lifetime than what estimated by TM 21 method especially for low currents and temperatures stresses. Also, constant lumen output drivers (CLOs) are designed based on proposed comprehensive formula and TM 21 lumen maintenance projection method and their efficacies are compared. According to lower lumen depreciation anticipation, less energy delivery to LED for compensating depreciation is needed for CLOs designed based on proposed formula. By less energy consumption, using proposed comprehensive formula can lead to less CO 2 emissions.

Stochastic Diffusion Modeling of Degradation Data

Accelerated degradation tests (ADTs) can provide timely relia bility information of product. Hence ADTs have been widely used to assess the lifetime distribution of highly reliable products. In order to properly predict the lifetime distribution, modeling the product’s degradation path plays a key role in a degradation analysis. In this paper, we use a stochastic diffusion process to describe the product’s degradation path and a recursive formula for the product’s lifetime distribution can be obtained by using the first passage time (FPT) of its degradation path. In addition, two approxi mate formulas for the product’s mean-time-to-failure (MTTF) and median life (B50) are given. Finally, we extend the proposed method to the case of ADT and a real LED data is used to illustrate the proposed procedure. The results demonstrate that the proposed method has a good performance for the LED lifetime prediction.

Monitoring the optical degradation of green light-emitting diodes on the basis of measured electrical characteristics

The degradation behavior and lifetime of LEDs for field operation is currently predominantly estimated using LM-80 data in combination with TM-21 extrapolations. If the environmental conditions differ significantly from the laboratory conditions of the LM-80 tests, differences in in-situ degradation behavior and TM-21 predictions could occur. Independently of the previous described methods, the following publication evaluates the use of an electro-optical model in order to allow an estimation of the in-situ degradation dynamics. The correlation between optical degradation and forward voltage decrease is determined on the basis of degradation tests performed on green high-power LEDs.Depending on the forward current selected, the correlation can be described by a linear or logarithmic function and can be used to build an electro-optical model that takes the degradation behavior for different operating conditions into account.A final validation of the model shows that the degradation behavior of individual LEDs can be determined, while a comparison of the measured mean values of four test LEDs with the model predictions shows a maximum root-mean-square error (RMSE) of 0.012. Accordingly, the method offers the possibility of condition monitoring that can be transferred into a practical measurement circuit.

The Implementation of Energy-Saving Lighting Systems for Poultry Houses

The provision of lighting in poultry shelters is an energy-intensive process in poultry farming, due to a lack of sunlight in closed facilities. Lighting plays an important role in the majority of organism biorhythms and it clocks the processes of vital activities of the birds. Lighting directly influences productivity, growth and sexual maturation of birds. A determining factor for the lifetime of an LED is the crystal heating temperature during its operation. It may be assumed that the LED lifetime is largely independent of the variation in the current passing through the LED (within the limits of its design values). The research objective was to conduct laboratory testing to compare the electricity consumption between the existing and a newly developed lighting system for poultry house no. 19 of the Kuchinsky Poultry Breeding Plant. In order to conduct the laboratory testing, the authors developed lighting fixtures consisting of sealed plastic bodies with an LED-carrying PCB inside. The testing continued for 113 days. The new system consumed 662 kWh, while the previous system consumed 783 kWh. Energy savings through the testing period amounted to 15%. During the testing, the new equipment was reliable; no failures of LED fixtures were recorded.
 Keywords: LED lighting, energy conservation, poultry farming, microclimate

Lifetime Prediction for a Cell-on-Board (COB) Light Source Based on the Adaptive Neuro-Fuzzy Inference System (ANFIS)

Predicting the lifetime of a LED lighting system is important for the implementation of design specifications and comparative analysis of the financial competition of various illuminating systems. Most lifetime information published by LED manufacturers and standardization organizations is limited to certain temperature and current values. However, as a result of different working and ambient conditions throughout the whole operating period, significant differences in lifetimes can be observed. In this article, an advanced method of lifetime prediction is proposed considering the initial task areas and the statistical characteristics of the study values obtained in the accelerated fragmentation test. This study proposes a new method to predict the lifetime of COB LED using an artificial intelligence approach and LM-80 data. Accordingly, a database with 6000 hours of LM-80 data was created using the Neuro-Fuzzy (ANFIS) algorithm, and a highly accurate lifetime prediction method was developed. This method reveals an approximate similarity of 99.8506% with the benchmark lifetime. The proposed methodology may provide a useful guideline to lifetime predictions of LED-related products which can also be adapted to different operating conditions in a shorter time compared to conventional methods. At the same time, this method can be used in the life prediction of nanosensors and can be produced with the 3D technique.

Experimental study of the LED lamp

LEDs are widely used light sources. Their main advantages are low power consumption, mechanical strength, high luminous efficacy, and a lifetime exceeding 50 000 hours. However, compared to other light sources, they are more sensitive to high temperatures. Heat is generated by converting electrical energy into radiant energy. The share of heat in this transformation describes the efficiency, but in the case of light sources, efficiency is not one of the basic parameters because only a part of the radiation produced is visible light, which interests the recipients. However, the temperature has a big influence on the properties and lifetime of LEDs. This article presents the results of temperature measurements of the LED lamp.

Enhanced photoactivity of BiVO4/Ag/Ag2O Z-scheme photocatalyst for efficient environmental remediation under natural sunlight and low-cost LED illumination

Bismuth vanadate (BiVO4, BV) is a promising visible-light responsive semiconductor photocatalyst able to harvest sunlight energy for photoelectrochemical and photochemical applications such as pollutants degradation and oxygen evolution from water. However, the fast recombination of photogenerated electrons and holes and poor electron transport properties remain as the bottlenecks in the way of efficient utilization of BV for such applications. Aiming to address these issues, we prepared Ag/Ag2O-loaded BV particles using a facile chemical deposition method employing an alkaline solution of glycerol for partial reduction (formation of Ag0) and deposition of Ag+ (as Ag2O) from AgNO3 solution. The as-prepared BV/Ag/Ag2O Z-scheme photocatalysts were characterized by SEM, TEM, DRS, XPS, XRD, Raman spectroscopy and electrochemical measurements. XRD and XPS analysis confirmed the formation of heterojunction photocatalysts of the type BV/Ag/Ag2O that show light absorption in an extended region of the visible spectrum as compared to pure BV. Compared to pristine BV (kobs. = 0.016 min-1), the synergy between the components in the resulting BV/Ag/Ag2O photocatalysts led to a dramatic increase (around 28 times) in photoactivity (kobs. > 0.45 min-1), as measured by photodegradation of crystal violet (CV) and Rhodamine B (RhB) employing commercial low-cost blue LEDs or natural sunlight. The enhanced photoactivity is attributed to the extended absorption of visible light and improved adsorption of dyes by the composite photocatalysts and the formation of BV/Ag/Ag2O Z-scheme heterojunction characterized by better charge carriers’ separation. Such a photocatalytic system highlights: (i) high efficiency aspect (since the emission of LEDs matches the absorption edge of BV) (ii) practicality aspects (the use of low-power, DC-operated LED photoreactor and natural sunlight) and (iii) economical aspects (low-cost and longer life-time of LEDs).

Cost-Effective LED Dimming Driver With Single Chip Design for Smart Lighting System

For smart lighting system, this paper presents a high-power (60V/1A) single-chip driver for LED dimming using TSMC high-voltage process. The main circuit included analog circuit, power driver and digital control circuit with mixing-mode design methodology. The proposed digital dimming controls LED brightness increasing or decreasing with only two switches. The switches can be controlled by the auto mode or manual mode for user selection. All digital control circuits are embedded to the chip. Because of without the need of micro-processor for LED dimming, this chip is cost-effective design that can save the components of interface. To keep high-stable LED lighting, the dimming techniques used current mode rather PWM (Pulse Width Modulation) to reduce flicker. The multi-level current approach used 16 steps for LED lighting control. The step resolution is 6.25% for smart lighting system. With variable constant current control, this approach can achieve better lighting efficiency, reduce noise radiation and prolong LED lifetime for smart lighting systems. The maximum driving efficiency of the proposed chip can achieve near 98% as driving for 60W LED dimming.

Power consumption control of LEDs considering their specific characteristics and ambient temperature variations

Ambient temperature is one of the factors affecting the luminous flux and the lifetime of LEDs. To consider this factor, In this study, the design and implementation of an innovative power control system of LEDs is presented. The distinct feature of the proposed system is its ability to use the information of the ambient temperature and the specific characteristic curves of LEDs. In the proposed method, a microcontroller unit controls the input power of the LED chipsets just by using the instant measured ambient temperature data, if the instant power is higher than the standard power (at 25 °C). The introduced system adjusts the input power and the light output of LEDs at temperatures below the standard ambient temperature of 25 °C. At the same time, this system preserves the standard lighting levels unchanged. Results of the calculations and implementation of the proposed system verify the efficiency of the developed method.

A Novel Approach for Reliability Investigation of LEDs on Molded Interconnect Devices Based on FE-Analysis Coupled to Injection Molding Simulation

Due to many advantages, such as cost-effective production, design freedom, and weight reduction, plastics have replaced metals and ceramics in many fields. However, engineering plastics are good thermal insulators. This characteristic, although beneficial in certain applications, poses many challenges in many heat-generating applications. This can lead to hot spots or even to an increase in the device temperature. Along with the increasing demand for plastics in areas of the lighting technology or in the automotive field due to the free shaping potential, the requirements are becoming more challenging. Driven by the trend of miniaturization, applications with high heat generation often have to operate in the tightest of spaces. Since not always sufficient space for complex cooling systems is given, the housing or the substrate should assume the task of thermal management. In regard to this fact, the use of thermally conductive thermoplastics seems to be very appealing. Quality loss, poorer reliability, loss of performance, and even failure can occur in case of insufficient heat dissipation. In order to improve the properties of these polymers, highly heat-conducting fillers are added in order to improve the thermal conductivity of the compound. Another technology trend that has been prevalent for years is the use of simulations. Due to shorter product life cycles and therefore shorter development times, simulation has become an indispensable part of the chain of product development. Time-consuming and costly test series make the simulation more and more important as a tool for material and product design. In this context, this paper presents a novel approach for reliability investigation and lifetime estimation, based on simulation. Therefore, a simulative method based on coupling the results from the process simulation (injection molding simulation) to finite element analysis was developed and explained. This coupled method makes it possible to take into account the manufacturing process and its engendered filler orientation. The obtained findings are compared to conventional thermal steady-state analysis and used in order to better predict the lifetime of LEDs mounted on thermoplastic substrates, the so-called molded interconnect devices. It is demonstrated that it is necessary to consider the filler orientation, especially in the case of 3D substrates.

New Dynamic Photo-Electro-Thermal Modeling of Light-Emitting Diodes With Phosphor Coating as Light Converter Part I: Theory, Analysis, and Modeling

Phosphor-coated light-emitting diode (PC-LED) is the dominant LED technology for public lighting. This paper presents a comprehensive theory for analyzing and modeling phosphor coating (PC) in white LEDs as a dynamic light converter. The new PC-LED model not only obeys the traditional diode equation but also includes the energy storage and transient effects of the PC. Major control variables include energy storage in and the luminous flux from the PC. This new model enables the dynamic variations of luminous flux and energy storage and power loss in PC to be accurately predicted. Part I of this paper provides the details of the theory and analysis leading to the new PC-LED model under the framework of the photo-electro-thermal theory. The details of the model parameter determination, model setup, and experimental verification are included in Part II. The model offers the important power loss equation of the PC which highlights the factors affecting the heat loss and the coating’s blackening effects. This equation can be used by engineers to design LED drivers in order to reduce the coating temperature and the blackening effects and to prolong LED lifetime.

Time evolution of packaged LED lamp degradation in outdoor applications

Degradation of Silicone used in high power white LEDs as molding material has significant impact on the LED's lifetime and efficacy. This work provides a detail study on the impact of moisture, temperature and thermal aging on the packaging materials by tracing its progression of degradation under high temperature and humidity conditions. Silicone degradation via discoloration and cracks formation is identified and its cracks depth is found to decrease as the time progressesdue to diffusion mechanism and this led to highly distorted surface. It is found that Silicone undergo hydrolysis, condensation, thermal oxidation and thermal aging over its lifespan, and discoloration is mainly due to hydrolysis while cracks formation is mainly due to thermal oxidation. The decrease in the crack depth is due to thermal aging where diffusion of silicon oligomer occurs.

A novel automated heat-pipe cooling device for high-power LEDs

In order to develop the thermal management of high-power LEDs, an automatic cooling device was firstly integrated with a microcontroller, heat pipes and fan. According to the experimental results, it was found that the substrate temperature of the high-power LEDs could be controlled automatically, and it could be kept in a relative low range to protect the LEDs, which contributes a better performance and longer lifetime of LED. A numerical model of the cooling system was established and its effectiveness was verified by experimental results. The simulation results show that the LED junction temperature can be maintained at a suitable range. Thus, the thermal resistances Rsa (from the heat sink to the ambient) and Rja (from the LED chip to the ambient) of the cooling system are 0.373°C/W and 5.953°C/W at 12W, respectively. In addition, increasing the number of heat pipes & cooling fins is an effective method to improve heat transfer of the cooling system. The proposed cooling system, whose total power consumption is less than 1.58W, is a very promising tool for the heat dissipation of high-power LEDs.

Optimal Design of Life Testing for High-Brightness White LEDs Using the Six Sigma DMAIC Approach

Life testing is an essential reliability assessment procedure to qualify a new product or technology before being released to the market. High-brightness white light-emitting diodes (HBWLEDs) with high efficiency, environmental benefits, and high reliability have attracted increasing interest in the field of lighting systems. However, owing to the long lifetime of LEDs, traditional life testing methods for LEDs, which record only failure time, are time consuming and expensive. Therefore, designing an optimal life testing process for HBWLEDs is desirable for accelerating LED technology innovation and development. This paper applies the Six Sigma define–measure–analyze–improve-control (DMAIC) approach to analyze the restrictions in the traditional life testing for HBWLEDs and optimize the life testing procedure. The goal is to shorten the testing time, reduce the testing operation cost, and maintain accurate reliability estimation. In this work, a general reliability estimation method with degradation data is developed by integrating a recursive unscented Kalman filter approach to estimate HBWLED reliability. The results show that, with the help of a recursive UKF, the accuracy of reliability estimation can be improved compared with the ordinary nonlinear least squares approach. Furthermore, the operation time and cost of LED life testing can be reduced by 57.75% and 71.51%, respectively, compared with traditional life testing.

Light Fades and Life Prediction of LED Light Source

The life is the most representative parameter in the parameters of LED reliability. But the impact factor of the LED lifetime are numerous and complicated, each factor of the influence degree of each are not identical. If according to the traditional light source life test method, then the cycle is too long to not led update speed. And the majority of the LED accelerated life test by means of increasing the should force experiments to estimate the life of the LED light source, this kind of test is usually elevated led where the ambient temperature or increasing the current through the LED itself. Finally, through the acquisition of data and analysis to predict the service life of LED light source, but did not direct theoretical foundation to justify force and the service life of LED light source specific equivalent relation. Therefore, the accuracy of accelerated stress measured the service life of LED light source is yet to be verified. Through the analysis of the change of the life of LED is a gradient of chemical reaction, with the Arrhenius model, led the life of the weakening is through changes in the flux to the lumen, and for that we can under the normal working condition analysis of LED light attenuation mechanism and rules, the prediction from but realize life led to predict led by degradation of cause and the change of life.

Layered Ceramic Phosphors Based on CaAlSiN3:Eu and YAG:Ce for White Light‐Emitting Diodes

To develop warm‐white light‐emitting diodes via conversion phosphors, blue light‐emitting diodes are generally combined with mixtures of green and red‐emitting phosphor powders. Generally, the phosphors are provided by resin embedded particle dispersions. Such resin‐based solutions cause several drawbacks with respect to LED lifetime and quality. Therefore, it has been investigated whether the red‐emitting nitride phosphor CaAlSiN3:Eu and the green‐emitting oxidic phosphor YAG:Ce can be cofired to layered ceramic composites. The shrinkage behavior and the composition of the interface in dependence of sintering temperature and the effect of interdiffusion processes at the interface on the luminescence properties were investigated. The formation of secondary phases at the interface in the cofired structures was found to limit the phosphor functionality for the nitride‐based CaAlSiN3:Eu in such composite ceramics. To counteract this, sacrificial interlayers were introduced to produce multilayered ceramics comprising CaAlSiN3:Eu and YAG:Ce for LED lighting applications. It is shown for the first time, that it is possible to sinter layered CaAlSiN3:Eu and YAG:Ce composite ceramics in a pressureless process at moderate sintering temperatures if one uses thin‐film passivated interfaces to reduce luminescence‐disturbing diffusion phenomena. These results demonstrate that diffusion barriers can be suitable means to obtain layered ceramic composites comprising CaAlSiN3:Eu and YAG:Ce in a pressureless sintering process with good optical properties.

A carbon footprint and energy consumption assessment methodology for UHI-affected lighting systems in built areas

This paper investigates the effects of urban heat island (UHI) on outdoor lighting systems in terms of GHG emissions: a novel methodology is proposed to assess the carbon footprint (CF) change of lighting services in built areas caused by UHI-induced ΔT with particular focus on the evaluation of the energy consumption. The methodology can be applied also to other activities affected by the UHI, such as HVAC and transport systems. In particular, ΔCF was introduced by a two-fold approach: the quantification of the CF change due to UHI (as difference between CF in an UHI-affected case and CF for an UHI-less case) and the CF change produced by a 1°C temperature change. A focus on LED lamps was developed: the lifetime of LEDs exponentially decreases with increasing temperature and the luminous flux exponentially decays with operation time. UHI (i.e. the increase in ambient temperature) affects the lifetime and the luminous flux of lamps producing higher energy consumption and higher replacement rates. Results showed that a positive ΔT due to UHI produces a positive ΔCF, which also becomes economically relevant in long-term scenarios. A case study was analyzed by applying the proposed methodology to Rome outdoor public lighting.

Analysis of LED Light Source Energy Consumption for Lighting System Optimized by BP Neural Network Based on Genetic Algorithm

To study influence of LED light source lifetime on electricity consumption, optimization of BP neural network is adopted to establish analysis model of energy consumption for neural network, regarding environmental illumination, LED working face illumination, attenuation rates of LED lifetime as input parameters and PWM as output parameters. Under future lifetime of LED, energy consumption is predicted through the model. Results show BP neural network based on genetic algorithm can calculate energy consumption of LED light source quickly and accuracy of prediction is high. The method can be well used to predict energy consumption of short-time LED.